1. Field of the Invention
The present invention relates generally to new and useful improvements in a rotatable abrading device of the type commonly referred to as centrifugal blasting machines, and more particularly to the throwing wheels and blade assemblies that are used in such machines.
2. Statement of the Prior Art
Centrifugal blasting machines comprising rotors or wheels having a plurality of blades installed thereon have been known in the art for many years. In use, a stream of abrasive particulate material is fed into the path of the rotating wheel from an impeller secured to the throwing wheel. The blades are adapted to receive and throw the abrasive from the periphery of the throwing wheel at an appropriate discharge point in the machine casing at a blasting velocity to strip or clean metal castings or the like. As the blades propel the abrasive material against a work surface, they are sometimes referred to as throwing blades. Due to the action of the abrasive material on the blades, the blades exhibit considerable wear over a period of time. Attempts have been made to fabricate the blades from abrasion-resistant alloys. In other cases, special blade configurations have been employed to minimize the effects of the abrasive material on the blades.
Notwithstanding these attempts to minimize wear and extend the life of the throwing blades, periodic blade removal and replacement is necessary. This maintenance results in a loss of valuable operating time. Furthermore, while the blades must be removable, they must also be held so securely that they will resist the tremendous centrifugal forces exerted on them when the wheel is operating.
Several methods have been proposed for securing the blades in a removable manner to the throwing wheel. One method involves securing the blades to the front side of a wheel disk, usually by means of a bolt or by means of radial grooves in the wheel, frequently of a dove-tail shape. Another method employs two wheel disks that are maintained in spaced-apart relation. Longitudinal narrow edges of the throwing blades are generally inserted into radial grooves arranged in opposing surfaces of the two disks. Auxiliary means, such as bolts, pivotal locking means, eccentrics, set screws, etc. can be employed to secure the blades against radial displacement. Examples of these devices can be found in U.S. Pat. No. 2,819,562, U.S. Pat. No. 3,352,064 and U.S. Pat. No. 3,654,736. In these devices blade replacement is not always easy because the blades “freeze” or become jammed in the grooves in which they are mounted.
Another arrangement is shown in U.S. Pat. No. 3,894,360. In this case, the blades are mounted on brackets having an angular cross-section, and the brackets, in turn, are mounted on the throwing wheel. The rear of each blade is provided with a cast-in insert stud, which is adapted for insertion through an opening in the angular bracket. The stud is provided with a slot adapted to receive a clip, which holds the blade in position on the angular bracket. The only securing means in this arrangement is comprised of the stud and the spring clip. Should either the stud or spring clip fail, such as by the blade wearing thin around the area of the stud, the blade will fly off the wheel.
Another arrangement is shown in U.S. Pat. No. 3,867,791. In this case, the throwing blade is secured to the wheel by means of a blade block, which is mounted on the wheel. Each blade block has a first groove near an inner end of the block and a second groove near an outer end. Each blade includes lugs for insertion in the grooves. There is a centrally disposed impeller that restricts the movement of the blades, particularly in a radial direction. This is accomplished by employing an impeller having a shoulder that contacts the inner end of the blade. While a degree of commercial success has been achieved with this device, the rear of the blade must generally be machined in the area where it contacts the impeller. This adds to the cost of the blades. Additionally, it has been found to be rather difficult to cast the blade of the type disclosed in the patent because of its large cross-sectional area.
A similar arrangement is shown U.S. Pat. No. 4,249,350. A throwing blade is attached to a throwing wheel by means of a blade block. The blade is attached to the blade block along the rear surface of the blade. Bolts are used to mount the blade block securely to the throwing wheel. An abutment means and protrusions are used to secure the blade in place in a chosen rotational direction. During periods when the wheel is not in operation, the blades are held to the blade blocks using locking springs which bias the blade so as to engage the protrusions and the abutment means.
This assembly has also achieved a measure of commercial success, but suffers from the additional costs and increased labor associated with blade block assembly designs. In addition, the rotational direction of the blade is predetermined to be either clockwise or counterclockwise in rotation, requiring direction specific replacement blades for a particular machine. These limitations further increase downtime and costs to the user.
In short, there exists a need in the art for an improved blade and an improved locking assembly for securing the blades to the wheel of a centrifugal blasting machine. The improved blades must be easily removed and replaced without the need for special tools or extensive disassembly of the device.
Preferably, the blades should not be susceptible to “shot freezing” or jamming in position due to fine particulate fouling the mounting mechanism, as is frequently encountered when the blades are installed in grooves in the abrasive blasting machine. The blades should be adapted to fit centrifugal blasting machines now on the market. The locking assembly should securely mount the blades on the throwing disk to prevent movement of the blades, especially in a radial direction. The assembly should be suitable for use with any length and width of blade turning in either direction. The assembly should not require the machining and the close tolerances characteristic of previous devices.